A comprehensive analysis of hippocampal interneurons is proposed in this application. Intracellular recording and staining methods will be used to identify and characterize various interneuron populations in the CA2-CA3a region of rat hippocampal slices (in vitro). The efects that these local circuit neurons exert on pyramidal cells will be studied during simultaneous intracellular penetrations of interneuron-pyramidal cell pairs. Interneuron influences on phyramidal cells will be compared to those of stimulus-induced synaptic inputs and pressure-ejected putative neurotransmitters. In other experiments, effects of various drugs (enkephalin, acetylcholine, kainate) and environmental treatments (hypoxia, repetitive stimulation) on interneurons will be investigated. Applying these morphological, electrophysiological, and pharmacological techniques, we can begin to study CNS neurons within the context of their functional circuits and local environments. Thus, it may be possible to gain a better understanding of the richness and complexity of CNS function.